A dynamic random access memory (DRAM) stores a bit of data on a capacitor in DRAM cells. The capacitors leak or pick up charge over time, and must be periodically refreshed for the DRAM to retain its data. Under normal operating conditions, the DRAM loses its data over a period of seconds after power has been removed from the DRAM. However, as the temperature of the DRAM decreases, the capacitors leak their charge at a slower rate. If the temperature is low enough, the DRAM may retain its data for minutes or hours after the DRAM has lost power.
The tendency of DRAM to retain its data at low temperatures after removal of power leaves it vulnerable to access by intruders. An intruder with physical access to a computer may bypass mechanisms that protect the computer against outside intrusion. A DIMM containing DRAM may be removed from the computer after the computer has powered down, transferred to another computer, and accessed for its data. This intrusion is a risk for any computer with DRAM, but especially so for a computer utilizing non-volatile storage encryption, as the DRAM could be accessed for the encryption keys to the storage that allow for continued access of the computer system. For example, a hard drive may be protected with an encryption algorithm that is enabled with an encryption key. However, if the hard drive was accessed in the last computer session, the encryption key may remain on the DRAM. The encryption key may be imaged and recovered by the intruder and the DRAM replaced into the original computer, without indication of hacking or access by the intruder.